Heavy equipment, such as load-haul-dump machines (LHDs), wheel loaders, carry dozers, etc., are used during an excavation process to scoop up loose material from a pile at a first location (e.g., within a mine tunnel), to haul the material to a second location (e.g., to a crusher), and to dump the material. A productivity of the excavation process can be affected by how well power produced by an engine of each machine is used to move material during the excavation cycle. In particular, the engine of the machine can be used to drive a pump that pressurizes fluid directed into or through actuators that propel the machine or move a work tool of the machine. When the actuators are powered by the pressurized fluid to move the material in a desired manner, the efficiency of the machine and the productivity of the process are both improved.
During machine and/or work tool movement, however, it may be possible for the actuators to stall. For example, during engagement of the work tool with a pile of material, it may be possible for the work tool to engage an immovable object. When this happens, the pump may still be pressurizing fluid and directing fluid to the actuator according to operator demand, but the actuator may not be capable of movement. While some of this fluid may find leak paths through the actuator, the majority of the fluid will be forced to spill over relief valves as fluid pressures associated with the actuator rise during the stall. The leakage and spillage of high-pressure fluid is wasteful and reduces the machine's efficiency.
One attempt to improve machine efficiency during stall is disclosed in U.S. Pat. No. 8,726,647 of Peterson et al. that issued on May 20, 2014 (“the '647 patent”). In particular, the '647 patent discloses a hydraulic control system having a first fluid actuator, a second fluid actuator, a pressure sensor, a velocity sensor, and a controller. The controller is configured to receive input indicative of a desired flow rate for the first fluid actuator, to determine an actual flow rate based on the velocity, and determine a stall condition of the first fluid actuator based on the desired flow rate, the actual flow rate, and the pressure. The controller is also configured to selectively divert fluid away from the first fluid actuator and to the second fluid actuator based on the stall condition of the first fluid actuator.
Although the hydraulic control system of the '647 patent may improve efficiencies during a stall condition by diverting otherwise wasted fluid away from a stalled actuator, the hydraulic control system may do little to remedy the stall condition.
The disclosed excavation system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.